Skinless porous particle PVC resin and process for producing same

ABSTRACT

Porous particles of vinyl resin are disclosed where said particles are non-spherical in shape, highly porous, skinless and friable. Processes are also disclosed for producing these novel particles. The particles are preferably PVC and exhibit an ability to absorb large amounts of plasticizer in a short time.

This is a division of application Ser. No. 038,099, filed Apr. 14, 1987,now U.S. Pat. No. 4,711,908, issued Dec. 8, 1987.

BACKGROUND OF THE INVENTION

Polyvinyl chloride (PVC) resins are used in large quantities throughoutthe world. Typically these PVC resins are produced by one of threeprocesses, suspension, emulsion or mass process. Emulsion produced PVCis very small in particle size such as 1 micron or less and isessentially non-porous. The emulsion process uses a relatively largeamount of surfactants to make the small particle resins. PVC resinsproduced by the mass process are much larger, having a weight averageparticle size of from about 100 to 300 microns. The mass resin isproduced in a process which normally does not use water and surfactants.The mass resin does not have a pericellular membrane around theparticle. The absence of the pericellular membrane offers someadvantages such as a purer product and faster uptake of plasticizer fora given porosity value of a resin, although mass resins are known fortheir low porosity.

By far the largest volume PVC resin is produced by the suspensionprocess. Suspension produced PVC resins have about the same particlesize and the same end uses as does mass produced resin. In thesuspension process, surfactants such as cellulose materials or partiallyhydrolyzed acetate which is usually referred to as polyvinyl alcohol(PVA) are used to suspend vinyl chloride monomer droplets in water andthe polymerization takes place in the monomer droplet usually aided by afree radical initiator.

In the suspension polymerization of PVC, droplets of vinyl chloridemonomer 30-150 microns in diameter are dispersed in water by agitationand aided by surfactants. A thin membrane is formed at the water tomonomer interface by dispersants such as PVA. This membrane has beenmeasured at 0.01 to 0.02 micron thick, and has been found to be a graftcopolymer of polyvinyl chloride and the dispersant(s). Early in thepolymerization, particles of PVC deposit onto the membrane from both themonomer and the water sides forming a skin 0.5-5.0 microns thick thatcan be observed on grains sectioned after polymerization. Primaryparticles which are about 1 micron in size deposit on the skin from themonomer side and water phase polymerized PVC at about 0.1 micron in sizedeposits on the water side of the membrane.

In suspension polymerization, droplets of polymerizing PVC, 30-150microns in size, agglomerate to form particles or grains of 100-200microns in diameter. With one droplet per particle the shape is quitespherical. When several droplets agglomerate to form one particle, theshape can be quite irregular and knobby sometimes referred to as popcornshaped.

Suspension produced PVC particles desirably have voids in the particlewhich is known as porosity. These voids (porosity) form when the variouscomponents of the particle agglomerate such as the primary particles anddroplets. Porosity is a very important property of the resin because itnot only allows the polymerized resin to be easily stripped of itsresidual monomer but also gives the resin the ability to absorb largequantities of plasticizers.

Not only is porosity important but also the particle shape is important.Spherical particles have several attributes such as fast extrusion andhigh bulk density. However, an agglomerated highly irregular particlehas better ability to absorb plasticizer quickly because of itsirregular shape.

When PVC particles are desired for a particular application whichrequires a "skinless" or "low skin" resin, then mass produced resin isusually the resin of choice. A previous suspension process was developedand is disclosed in U.S. Pat. No. 3,706,722 to Nelson, et al, whichproduces resin particles having "low skin" features. The term "low skin"as used herein refers to resin particles having less than 50% of theirsurface area as PVC as measured by ESCA technique. This process is knownas a phase inversion process. In the early part of the polymerization,the monomer is the continuous phase and after about 10% conversionadditional water is added such as to make the water the continuous phaseand the monomer the discontinuous phase. This process in essence runs amass type polymerization up to about 10% conversion and then inverts toa suspension type polymerization. The resultant resin particle, however,is a porous spherical shape particle and not the more desirable porousagglomerated irregular shape particle. Also, the prior inversion processresults in very heavy polymer buildup on the internal surfaces of thepolymerization equipment. This buildup is sometimes referred to asreactor fouling and is a highly undesirable feature.

It would be very desirable to have a PVC resin particle which would beskinless, highly porous, friable, have fast plasticizer uptake and havean agglomerated shape.

SUMMARY OF THE INVENTION

It is an object of this present invention to produce PVC resin inparticulate form which are non-spherical, highly porous, friable andwhich are skinless or low-skin resins.

It is a further object of this invention to produce PVC resins whichhave short powder mix times.

It is a still further object of this invention to provide improvedprocesses to produce the above skinless or low-skin resin particles.

It is another object of this invention to provide processes which willproduce skinless or low-skin resins while preventing polymer buildup orscale on the internal surfaces of the polymerization equipment.

These and other objects will become apparent from the followingdescription of the invention.

An agglomerated, highly porous, friable, skinless PVC resin inparticulate form characterized by more than about 90% by weight of saidresin particles having the following features:

(a) an agglomerated non-spherical shape having a shape factor less thanabout 0.85, preferably less than about 0.83, more preferably less thanabout 0.80;

(b) said particles are absent a substantially continuous pericellularmembrane.

It is also preferred that more than 90% of said resin particles have thefollowing features:

(c) a mercury porosity of from about 0.1 cc/g to about 0.7 cc/g,preferably from about 0.3 cc/g to about 0.5 cc/g;

(d) a weight average particle size of from about 70 microns to about1000 microns, preferably from about 100 microns to about 250 microns;

(e) a friability less than about 2, preferably less than 1, morepreferably 0;

(f) a powder mix time of less than about 400 seconds, preferably lessthan 300 seconds, more preferably less than 250 seconds;

(g) the surface area of said particles is greater than about 20% PVC,preferably greater than about 50%, more preferably greater than about60% as measured by ESCA.

An improved process is provided for producing the novel particles ofthis invention comprising polymerizing vinyl chloride monomer in anagitated aqueous suspension wherein said aqueous medium contains as theprimary dispersant small amounts of at least one ionic sensitivedispersant capable of thickening water and at least one secondarydispersant, wherein an ionic material is charged to the polymerizationmedium at from about 1% to 5% conversion of monomer to polymer and theionic material desorbs a substantial amount of the ionic sensitiveprimary dispersant off the monomer droplet, thereby producing askinless, agglomerated, highly porous, friable, PVC resin absent acontinuous pericellular membrane.

An alternate improved process is also provided for producing the novelparticles of this invention comprising polymerizing vinyl chloridemonomer in an agitated aqueous suspension wherein said aqueous mediumcontains at least one primary dispersant capable of thickening water andat least one secondary dispersant wherein the levels of the primary andsecondary dispersants are at very specific amounts such that acontinuous pericellular membrane (skin) is not present on the resinparticle.

A process to produce the low-skin resins of this invention is alsoprovided. The low-skin process involves using extremely low levels offrom about 0.01 to about 0.03 part by weight per 100 parts by weight ofpolymerizable monomer, of the water thickening primary dispersant(s)along with monomer-soluble secondary dispersants.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photomicrograph of agglomerated, irregular shaped, highlyporous resin particles of this invention magnified 100 times actualsize. The particles of FIG. 1 were produced in Example I.

FIG. 2 is a photomicrograph of a particle produced in Example I (same asFIG. 1) with a magnification of 500 times actual size.

FIG. 3 is a photomicrograph of the particle of FIG. 2 magnified 5000times actual size.

FIG. 4 is a photomicrograph of agglomerated, irregular shaped, highlyporous resin particles of this invention magnified 100 times actualsize. The particles of FIG. 4 were produced in Example II.

FIG. 5 is a photomicrograph of a particle produced in Example II (sameas FIG. 4) with a magnification of 500 times actual size.

FIG. 6 is a photomicrograph of the particle of FIG. 5 magnified 5000times actual size.

FIG. 7 is a photomicrograph of an agglomerated, irregular shaped resinwith a skin essentially continuous over the resin particles' surface.This FIG. 7 represents a standard pipe grade suspension process producedPVC resin having a skin. FIG. 7 is magnified 100 times actual size.

FIG. 8 is a photomicrograph of a particle of the resin of FIG. 7magnified 500 times actual size.

FIG. 9 is a photomicrograph of an agglomerated, non-spherical porousresin with a skin essentially continuous over the resin particlesurface. This FIG. 9 represents a standard film grade suspension processproduced PVC resin. FIG. 9 is magnified 100 times actual size.

FIG. 10 is a photomicrograph of a particle of the resin of FIG. 9magnified 500 times actual size.

FIG. 11 is a photomicrograph of an agglomerated, non-spherical porousresin with low-skin magnified 100 times. The resin in FIG. 11 wasproduced in Example X.

FIG. 12 is a photomicrograph of a resin particle in FIG. 11 magnified500 times actual size.

DETAILED DESCRIPTION

Polyvinyl chloride resin as used in this invention means polyvinylchloride homopolymers as well as vinyl chloride polymerized with up to50%, preferably up to 20%, by weight of one or more other vinylidenemonomers having at least one terminal CH₂ ═C< grouping. Suitablecomonomers that may be polymerized with vinyl chloride are esters ofacrylic acid, for example, methyl acrylate, ethyl acrylate, butylacrylate, octyl acrylate, cyanoethyl acrylate, and the like; vinylacetate; esters of methacrylic acid, such as methyl methacrylate, ethylmethacrylate, butyl methacrylate, and the like; styrene and styrenederivatives including α-methyl styrene, vinyl toluene, chlorostyrene;vinyl naphthalene; diolefins including butadiene, isoprene, chloroprene,and the like; and mixtures of any of these types of monomers and othervinylidene monomers copolymerizable therewith; and other vinylidenemonomers of the types known to those skilled in the art. The amount ofcomonomer that can be polymerized with vinyl chloride is a function ofthe choice of comonomer, as is well understood by those skilled in theart. Preferably, the polyvinyl chloride polymers of this invention arepolyvinyl chloride homopolymers. The invention will be described interms of a polyvinyl chloride homopolymer as the preferred embodiment ofthis invention.

The process used to produce the novel resin particles of this inventionis an agitated aqueous suspension process. In the process, water is thepolymerization medium and a vinyl monomer to water ratio in the range ofabout 1.0:1.0 to 1.0:10.0 is satisfactory. Preferably, a ratio in therange of about 1.0:1.0 to 1.0:4.0 is employed.

An important feature of the process to prepare the resin particles ofthis invention is the dispersant system that is employed in thepolymerization reaction for the purpose of stabilizing the dispersedmonomer droplets. A colloidal unstable system will result in what isknown as a solid charge, that is, the monomer droplets will agglomerateinto large chunks which are unsuitable for use in normal PVCapplications. A dispersant system which will not allow any agglomerationof monomer droplets will result in spherical particles. Such a processto produce spherical particles is described in U.S. Pat. No. 4,603,151.To obtain an agglomerated particle of this invention requires a delicatebalance of having a few of the monomer droplets agglomerate but notexcessive agglomeration such as to result in excessively largeparticles. An important component of this process is an ion sensitivedispersant which will thicken water. Examples of such thickeners and howthey are used are disclosed in U.S. Pat. No. 3,620,988, incorporatedherein by reference. The ion sensitive dispersants which will thickenwater are usually high molecular weight dispersants or crosslinkeddispersants which will thicken water at concentrations of less than 2%in water, preferably less than 0.2%, and more preferably less than 0.1%concentration in water. Suitable ion sensitive thickening dispersantsinclude crosslinked polyacrylic acid polymers, crosslinked ethylenemalic anhydride polymers, high molecular weight uncrosslinkedpolyacrylic acid polymers and ethylene malic anhydride polymers, and thelike. The invention will be explained in connection with a substantiallyunneutralized crosslinked interpolymer.

A suitable ion sensitive thickener is a substantially unneutralizedcrosslinked interpolymer of one or more carboxylic acid monomers with apolyunsaturated compound having a plurality of terminally unsaturatedpolymerizable groups, for example, a crosslinked polyacrylic acidpolymer. The crosslinking is responsible for making the polyacrylic acidpolymer incapable of forming a true solution in water. In this regard,these polyacrylic acid polymers are classified as being substantiallyinsoluble in water. Nevertheless, the structure of the interpolymer mustbe such that it has enough affinity for water to swell appreciably in anaqueous medium, thus thickening the water phase, but not to the extentthat it cannot be agitated rapidly. Interpolymers that have little or noaffinity for water and do not swell to any measurable degree, are notsuitable for the purpose of the present invention.

With respect to the crosslinked polymeric dispersants used in making theresin of the invention, the carboxylic acid monomers utilizable inpreparing the same are those which contain at least one activecarbon-to-carbon double bond in the α,β-position with respect to acarboxyl group such as ##STR1## wherein R' is hydrogen or a --COOHgroup, and each of R" and R"' is a hydrogen or a monovalent substituentgroup which is linked to one of the doubly bonded carbon atoms.Carboxylic acids within this definition include acids, such as acrylicacid, wherein the double bond is terminal such as ##STR2## or thedicarboxylic acids such as maleic acid and other anhydrides of thegeneral structure ##STR3## wherein R and R' are monovalent substituentgroups and especially those selected from the group consisting ofhydrogen and halogen groups and alkyl, aryl, alkaryl, aralkyl, andcycloaliphatic radicals.

Included within the class of carboxylic acids, shown by generic formula(1) above, are widely divergent materials, such as the acrylic acids,such as acrylic acid itself, methacrylic acid, ethacrylic acid, α- andβ-chloro and bromo-acrylic acids, crotonic acid, maleic acid, itaconicacid, and many others.

Polymerizable carboxylic anhydrides include any of the anhydrides of theabove acids, including mixed anhydrides, and those shown by genericformula (3) above, including maleic anhydride, and others. In manycases, it is preferred to copolymerize an anhydride monomer with acomonomer, such as methyl vinyl ether, styrene, ethylene, and the like.

It is preferred to employ polymeric dispersants which are derived frompolymers produced by the polymerization of the α,β-monoolefinicallyunsaturated carboxylic acids. The preferred carboxylic acids are thosederived from the acrylic acids and α-substituted acrylic acids havingthe general formula ##STR4## wherein R is a monovalent substituentselected from the group consisting of hydrogen, halogen, hydroxyl,carboxyl, amide, ester, lactone, and lactam.

The most preferred polymeric dispersants are those prepared from thelightly crosslinked interpolymers of acrylic acid. These dispersants arethe most effective.

The crosslinking agents which may be employed with any of the carboxylicmonomers, or mixtures thereof, may be any compound, not necessarilymonomeric in nature, containing two or more terminal polymerizable CH₂═C< groups per molecule. Examples of this class of materials includepolyunsaturated-hydrocarbons, -polyethers, -polyesters, -nitriles,-acids, -acid anhydrides, -ketones, -alcohols and polyunsaturatedcompounds of this class incorporating one or more of these and otherfunctional groups. Specifically, there may be utilized divinyl benzene,divinyl naphthalene, low-molecular weight and soluble polymerizeddienes, such as polybutadiene and other soluble homopolymers of openchain aliphatic conjugated dienes, which soluble polymers do not containany appreciable number of conjugated double bonds, and otherpolyunsaturated hydrocarbons; polyunsaturated esters, ester-amides andother ester derivatives, such as ethylene glycol diacrylate, ethyleneglycol dimethacrylate, allyl acrylate, methylene bisacrylamide,methylene bismethacrylamide, triacrylyl triazine, hexallyl trimethylenetrisulfone, and many others; polyunsaturated ethers, such as divinylether, diallyl ether, dimethyl allyl ether, diallyl ethylene glycolether, diallyl, triallyl and other polyallyl ethers of glycerol,butene-1,2-diol, 1-phenyl-1,2,3-propanetriol, the polyallyl, -vinyl and-crotyl polyethers containing from two to seven or more of these orother alkenyl ether groupings per molecule and made from polyhydricalcohols, such as the carbohydrate sugars, and the so-called "sugaralcohols", including erythritol, pentaerythritol, arabitol, iditol,mannitol, sorbitol, inositol, raffinose, glucose, sucrose, and manyothers, and other polyhydroxy carbohydrate derivatives, thecorresponding polyalkenyl silanes, such as the vinyl and allyl silanes,and others. Of this large class of crosslinking agents, the polyalkenylpolyethers of the carbohydrate sugars, sugar alcohols and otherpolyhydroxy carbohydrate type derivatives containing from two to sevenalkenyl ether groups per molecule are particularly useful. Suchmaterials are easily prepared by a Williamson-type synthesis involvingthe reaction of an alkenyl halide, such as allyl chloride, allylbromide, methallyl chloride, crotyl chloride, and the like, with astrongly alkaline solution of one or more of the poly-hydroxycarbohydrate derivatives.

In the monomeric mixture, for making the crosslinked polymers employedas primary dispersants in the suspension polymerization process used inthis invention, the two essential monomeric materials should be presentin certain proportions, although the exact proportions will varyconsiderably depending on the characteristics desired in the polymer.Small amounts of the polyalkenyl polyether copolymerize quite readilywith carboxylic monomers and the crosslinking effect of the polyalkenylpolyether on the carboxylic monomer is so strong that as little as 0.1%by weight thereof, based on the weight of the total mixture, produces agreat reduction in the water and solvent-solubility of the resultingcrosslinked polymer. When 0.1% to 4.0%, more preferably 0.20% to 2.5%,by weight of the polyether is utilized, water-insoluble polymers areobtained, especially with acrylic acids, which are extremely watersensitive. Useful dispersants are also obtained when 0.1% to 6.0%, andpreferably 0.2% to 5%, of the polyether is copolymerized with maleicanhydride. In the dual copolymer, or two-compound interpolymer, thismeans that the remainder of the monomeric mixture will be the carboxylicmonomer.

The monomeric proportions employed in the production of multi-componentinterpolymers may vary in a somewhat similar manner. However, it isgenerally desirable to utilize as much of the carboxylic monomer ormonomers and as little of the other monomeric constituents as isconsistent with the desired water-insolubility and other properties. Inthese interpolymers, therefore, the carboxylic monomer or monomerswhould never be less than 25%, and preferably not less than 40%, byweight of the total monomeric mixture. Multicomponent interpolymers maybe made from monomeric mixtures comprising from 25% to 95% of acarboxylic monomer, such as acrylic acid, 0.1% to 30% of a polyalkenylpolyether, such as polyallyl polyether of sucrose, and 5.0% to 74.9% ofan additional monomer or monomers. Preferred multi-componentinterpolymers are the tripolymers resulting from the polymerization ofmonomeric mixtures containing, respectively, from 40% to 95% by weightof acrylic acid, 0.20% to 2.5% by weight of polyallyl polyether, such asthat of sucrose, and 4% to 59% of an additional monomer or monomers,such as maleic anhydride, N-methyl acrylamide, methyl vinyl ether, ethylvinyl ether, n-butyl vinyl ether, and the like, and mixtures of maleicanhydride, a vinyl alkyl ether, such as vinyl methyl ether, and apolyallyl polyether, in which the sum of the moles of vinyl ether andpolyallyl polyether is substantially equivalent to the molar quantity ofmaleic anhydride present. It should be borne in mind that in the aboveproportions, if a maximum amount of two of the monomers are utilized,that somewhat less than maximum amounts of the other monomers must beutilized.

Suitable for use as additional monomers in the production ofmulti-component interpolymers are monoolefinic vinylidene monomerscontaining one terminal CH₂ ═C< group, such as styrene, the chloro andethoxy-styrenes, etc., acrylamide, N-methyl-acrylamide, N,N-dimethylacrylamide, acrylonitrile, methacrylonitrile, methyl acrylate, ethylacrylate, 2-ethylhexylacrylate, methyl methacrylate, vinyl acetate,vinyl benzoate, vinyl pyridine, vinyl chloride vinylidene chloride,vinylidene chlorobromide, vinyl carbazole, vinyl pyrrolidone, methylvinyl ether, ethyl vinyl ether, n-butyl vinyl ether, methyl vinylketone, ethylene, isobutylene, dimethyl maleate, diethyl maleate, andmany others. In addition to the above monoolefinic monomers, many of thedivinyl dialkenyl or other polyfunctional esters, amides, ethers,ketones, and the like, may be used in the production of multi-componentinterpolymers, especially those polyfunctional monomers which nominallyfunction as crosslinking or insolubilizing monomers but which are easilysaponified and hydrolyzed to additional hydroxyl, carboxyl and otherhydrophilic groups. For example, an interpolymer of acrylic acid anddivinyl ether is insoluble in water but upon standing gradually goesinto solution probably due to hydrolysis and breaking of divinyl ethercrosslinks. The presence of strong alkali or acid speeds dissolution.Spectroscopic analysis confirms the presence in the polymers ofnon-carboxylic hydroxyls. Similarly, diesters, such as diallyl maleate,ethylene glycol dimethacrylate, acrylic anhydride, betaallyloxyacrylate, and many others, are readily saponified or hydrolyzed byalkali or acid with the introduction of additional hydroxyl and/orcarboxyl groups. Of the additional monomers, N-methyl acrylamide, methylvinyl ether, ethyl vinyl ether and divinyl ether have been foundparticularly useful in the production of the substantially unneutralizedcrosslinked interpolymers for use as ion sensitive dispersants in thesuspension polymerization of vinyl monomers.

The amount of the water-insoluble substantially unneutralizedcrosslinked interpolymer useful as an ion sensitive dispersant, in theprocess of making the novel resins of this invention will vary in therange of about 0.01 parts by weight to about 0.1 parts by weight, basedon 100 parts by weight of the monomer or monomers being polymerized.Preferably, the amount used will be in the range of about 0.02 parts byweight to about 0.06 parts by weight per 100 parts by weight of monomeror monomers being polymerized.

In the process to make the novel resins of this invention, othersecondary dispersants are preferably employed, along with the ionsensitive dispersant. Dispersants which tend to form a skin on the resinparticles such as methyl cellulose and high hydrolysis (above 70%)polyvinyl acetate should be avoided. The secondary dispersants should bemonomer soluble and not fully soluble in water. For PVA secondarydispersants, the higher the % hydrolysis, the more water soluble thedispersant. For example, 30% hydrolyzed PVA is monomer soluble and notwater soluble, 55% hydrolyzed PVA is very soluble in the vinyl monomerbut is also partially soluble in water. 72.5% hydrolyzed PVA is fullywater soluble and therefore not acceptable. The fully water solubledispersants will form a skin on the polymer particle. Oil-solublenon-polyethylene oxide containing secondary dispersants are suitable foruse in this invention. Suitable non-polyethylene oxide containingsecondary dispersants are those compounds from the sorbitan ester familyor the glycerol ester or polyglycerol ester families, as well as the lowhydrolysis (less than 70%, preferably less than 60%, and more preferablyless than about 55%) polyvinyl acetates, which do not containpolyethylene oxide segments. As examples of such dispersants, there maybe named sorbitan trioleate, sorbitan tri-stearate, sorbitan monooleate,sorbitan monopalmitrate, glycerol monooleate, glycerol monostearate,triglycerol monooleate, 50% hydrolyzed polyvinyl acetate, and the like.A mixture of more than one of these dispersants may be used. Thefunction of the secondary dispersants is to increase the porosity of thepolymer particles and to increase the colloidal stability of thepolymerization mixture. The non-polyethylene oxide containing dispersantis used at a level of from about 0.005 part by weight to about 1.0 partby weight per 100 parts by weight of monomer, preferably from about 0.1part by weight to about 0.4 part by weight per 100 parts by weight ofmonomer. More than one secondary dispersant may be used in thisinvention to achieve the secondary dispersant level.

The polymerization is initiated with a free radical catalyst. Themonomer-soluble or oil-soluble catalysts that may be used in thepolymerization process of this invention are the alkanoyl, aroyl,alkaraoyl, and aralkanoyl diperoxides and monohydroperoxides, azocompounds, peroxy ester, percarbonates, and other free radical typecatalysts. As examples of such catalysts, there may be named benzoylperoxide, lauryl peroxide, diacetyl peroxide, cumene hydroperoxides,methyl ethyl ketone peroxide, diisopropylbenzene hydroperoxide,2,4-dichlorobenzoyl peroxide, naphthoyl peroxide, t-butyl perbenzoate,di-t-butyl perphthalate, isopropyl percarbonate, acetyl cyclohexanesulfonyl peroxide, disecondary butyl peroxydicarbonate, 5-butylperoxyneodecanoate, di-normal propyl peroxydicarbonate, azo-bisisobutyronitrile, α,α'-azodiisobutyrate, 2,2'-azo-bis-(2,4-dimethylvaleronitrile), and many others. The particular free radical catalystemployed will depend upon the monomeric material(s) being polymerized,the molecular weight and color requirements of the polymer, thetemperature of polymerization, etc. Insofar as the amount of catalystemployed is concerned, it has been found that an amount in the range ofabout 0.005 parts by weight to about 1.00 parts by weight, based on 100parts by weight of the monomer or monomers being polymerized, issatisfactory. However, it is preferred to employ an amount of catalystin the range of about 0.01 part by weight to about 0.20 part by weightbased on 100 parts by weight of monomer(s).

The suspension polymerization process of this invention may be carriedout at any temperature which is normal for the monomeric material to bepolymerized. Preferably, a temperature in the range of about 0° C. toabout 100° C. is employed, more preferably from about 40° C. to about80° C. In order to facilitate temperature control during thepolymerization process, the reaction medium is kept in contact withcooling surfaces cooled by water, brine, evaporation, etc. This isaccomplished by employing a jacketed polymerization reactor wherein thecooling materials is circulated through the jacket throughout thepolymerization reaction. This cooling is necessary since most all of thepolymerization reactions are exothermic in nature. It is understood, ofcourse, that a heating medium can be circulated through the jacket, ifnecessary.

The preferred process to produce resins of this invention involves usingan ionic material to desorb the primary dispersant off the resin.Suitable ionic materials are bases which will neutralize the polyacrylicacid primary dispersant and form a salt. Preferably, the ionic materialis a monovalent inorganic or organic base such as amines, sodiumhydroxide, ammonium hydroxide, potassium hydroxide, lithium hydroxide,and the like. The most preferred ionic material is sodium hydroxide.Divalent and trivalent materials can crosslink the polyacrylic acidprimary dispersant and would therefore not normally be chosen as theionic material. The preferred embodiment of this invention will bedescribed in terms of using sodium hydroxide as the ionic material. Theprimary dispersant protects the monomer droplets at the very earlystages of polymerization. Before the primary dispersant can graftpolymerize with the vinyl chloride, NaOH is added to the polymerizationmedium. The ion sensitive primary dispersant will then swell in size anddesorb off the droplet. Protection of the droplet is accomplished afterthis point by the increased size of the primary dispersant. The NaOHmust be added early in the polymerization, usually from 0.5% to 5.0%conversion of monomer to polymer. If the NaOH is added at the beginningor before about 0.5% conversion, the primary dispersant will be desorbedoff the droplet too early and could result in an unstable suspension.Preferably the NaOH is added at from 1% to 3% conversion, morepreferably 1% to 2% conversion. Since the primary dispersant is desorbedfrom the droplet and polymerization is continued without a primarydispersant on the particle, the resulting resin is essentiallyskin-free. Of course, some primary dispersant can become attached to theresin particle without departing from this invention but there cannot bea continuous pericellular membrane present as there is in normalsuspension PVC resin.

The amount of NaOH typically added is an amount sufficient to raise thepH about 0.5 to 1.0 point. Usually the amount of NaOH needed to desorbthe primary dispersant is from about 0.0010 part by weight to about0.0100 part by weight per 100 parts of monomer. More could be used butit would not serve a useful purpose.

If an ion sensitive dispersant is used which will thicken by loweringpH, then rather than adding NaOH to desorb the dispersant, HCl could beused. The HCl would work in the same fashion as described above andshould be added at similar low conversion levels as described above.

An alternate process to produce the low skin resins of this invention isto use extremely low levels of the ion sensitive primary dispersant.Levels of from about 0.01 to about 0.03 parts by weight per 100 parts byweight of polymerizable monomer should be used in this alternate method.If these low levels are used, then it is not necessary to use the NaOHto desorb the primary dispersant from the monomer droplet. Secondarydispersants at levels described above are used in this alternate method.

An additional alternate process to produce the resins of this inventioninvolves the use of a combination of dispersants. The combination ofdispersants are non-polyethylene oxide containing secondary dispersantssuch as sorbitan esters, for example sorbitan monooleate andnon-polyethylene oxide containing dispersants such as low hydrolysisPVA, and primary dispersant polyacrylic acid. Sorbitan esters areeffective porosifiers but in amounts greater than 0.1 part they tend tobe highly destabilizing. It was also found that higher levels of about0.2 to 0.4 part of sorbitan ester would prevent the formation of a skinby the primary dispersant. It was also unexpectedly found that lowhydrolysis PVA (less than 70%, preferably less than 60%, more preferablyless than about 55%) in amounts of from about 0.1 to 0.3 part by weightwould counteract the destabilizing effect of sorbitan ester. The levelof polyacrylic acid dispersant used in this process to give skinlessresin will vary depending upon the level of PVA. For levels of PVA ofabout 0.3 part, the polyacrylic acid dispersant needs to be less than0.04 part, whereas for levels of PVA of about 0.1, the level ofpolyacrylic acid dispersant can be higher, such as about 0.06. As thelevel of PVA increases, the level of polyacrylic acid dispersant mustdecrease to obtain a skinless resin. High hydrolysis PVA's greater than70% and dispersants such as methyl cellulose should be avoided becausethey will form a skin on the resin.

Reactor Charging Procedure

In the preferred process to produce skinless resins of this invention, acharging procedure similar to the one disclosed in my U.S. patentapplication Ser No. 846,163 filed Mar. 31, 1986, incorporated herein byreference, should be used. The procedure used is what is known as a onepoly floating method. The free radical catalyst is first mixed with asolvent, such as isopropol alcohol, in the preferred process. Thistechnique of using a catalyst solution and its added benefits are fullydisclosed in the above incorporated patent application. Thepolymerization reactor charging procedure is explained in the stepsbelow.

(a) Charge water and ion sensitive primary dispersant(s) capable ofthickening water to the polymerization vessel. The primary dispersant(s)can be added as such but is preferably added as a concentrated mixturewith water. The water and primary dispersant(s) may be premixed beforecharging to the polymerization vessel. The charge water is preferablydemineralized water.

(b) Agitate the water and primary dispersant(s) until an emulsion isformed.

(c) Reduce or stop the agitation such that non-turbulent flow isachieved.

(d) Charge the monomer(s) to be polymerized to the reactor vessel suchthat said monomer floats on top of the emulsified thickened aqueouslayer.

(e) Charge a solution comprising a solvent and the free radical catalystand optionally the secondary dispersant(s) to the reactor. If thesecondary dispersant(s) are not combined with the catalyst solution,then they should have been premixed with the monomer before adding tothe reactor.

(f) Allow the catalyst solution to diffuse through the monomer layer.

(g) Increase the agitation such that the entire polymerization medium isemulsified.

(h) Conduct to polymerization until 1% to 2% conversion is reached, thenadd NaOH to desorb the primary dispersant from the monomer droplet.

(i) Continue the polymerization until the desired degree ofpolymerization is achieved.

An alternate charging method, known as the two poly method, is to firstadd the monomer(s) to the reactor together with the solution containingthe catalyst and secondary dispersant(s). The catalyst solution could,of course, be premixed with the monomer prior to adding to the reactorvessel, in which case agitation would not be necessary after adding tothe reactor. This mixture is then agitated thoroughly. The thickenedwater, which had been previously made up by mixing the ion sensitivethickening primary dispersant(s) with water, is charged into the bottomof the reactor through a bottom entry port. Agitation is then re-startedand polymerization conducted as above.

The catalyst could also be charged neat into the water phase containingthe primary dispersant. If this method were used, then the catalystwould not first be premixed with the solvent.

The polymer particles produced by the present invention should have anaverage diameter by weight greater than about 70 microns. The particlescould have an average diameter up to 1000 microns but normally, thepolymer particles will have an average diameter by weight less thanabout 300 microns. Preferably, for most end uses, the polymer particleswill have a diameter in the range of about 100 microns to about 250microns, most preferably from about 125 microns to about 200 microns.Resins with an average particle size by weight less than 70 microns tendto be dusty and build up static easily such that they are lessdesirable.

The resin particles produced by this invention are agglomeratednon-spherical in shape. A very good method to measure the sphericalshape of resins is to determine the shape factor by optical procedures.The image of the particle is projected onto a flat surface to provide atwo dimensional view. The shape factor of a particle is determined byinscribing and circumscribing the resin particles flat image with acircle. The ratio of the diameters of the inscribed circle to thecircumscribed circle is the number known as the shape factor.

In the case of a perfect circle, the inscribed and circumscribed circleswould have the same diameter and, therefore, the shape factor would beunity (1.0). The more near the shape factor is to 1.0 the more sphericalthe particle.

The shape factor of the resin particles made by this invention is lessthan about 0.85, preferably less than about 0.83, and more preferablyless than about 0.80.

The resin particles made by this invention also have high porosity offrom about 0.10 cc/g to about 0.7 cc/g as measured using mercuryporosimeter. Preferably, the mercury porosity is from about 0.30 cc/g toabout 0.50 cc/g. Porosity is measured according to ASTM D-2873procedure. Sometimes porosity is measured as DOP porosity, which givesresults about 0.02 cc/g higher than mercury porosity values reportedherein for the same resin.

The resins of this invention must also be low-skin or skinless. Theterms low-skin and skinless as used in this specification mean that theresin does not have a continuous pericellular membrane as does a typicalPVC resin. There may be discontinuous areas or spots of skin on theresin surface but the resin would still be considered skinless under themeaning used in this invention. The term low-skin is used to refer toparticles having less than 50% PVC on their surface whereas the termskinless refers to particles having 50% or greater PVC on their surface.

One method to characterize skinless resins is determine the compositionof the surface of the resin particle by use of XPS (ESCA) technique. Ifa resin was totally skinless, there would not be any primary dispersanton the surface. The surface of the resins of this invention will haveless than 40%, preferably less than 25%, and more preferably less than10%, of the primary dispersant, as measured by ESCA technique. Thesurface will consist mainly of PVC and secondary surfactants(porosifiers).

The resin particles of this invention have a surface composition asmeasured by ESCA greater than about 20% PVC, preferably greater thanabout 50%, more preferably greater than about 60%. This indicates thatthe particles have a significant portion of holes in their skin, wheresaid holes allow the plasticizer to easily pass into and be absorbed bythe particle. ESCA is an acronym that stands for electron spectroscopyfor chemical analysis. The ESCA technique involves irradiating thesample with X-rays from an X-ray tube. The x-rays knock electrons out ofthe atoms that are on the surface of the sample. The energy and numberof these electrons are measured. From that information one can determinewhat elements are present. The depth of analysis of ESCA is about 20 to30 angstroms which is about 5 or 6 monolayers of atoms on the surface ofa sample. One should keep in mind that the ESCA test conducts ananalysis of the surface visible to the ESCA. In a skinless or low skinresin, pores are open to the surface, therefore the X-rays are goinginto the pores and the results reflect an analysis of the bottom of thepore as well as the outermost surface of the resin particle. Thisexplains to a great deal why the ESCA analysis of a skinless resin showsthe secondary dispersant present. The secondary dispersant is believedto be present on the primary particles which are visible when lookinginto the pores. The interior of the pores can be seen from the 5000magnification photomicrographs of FIG. 3 and FIG. 6.

Another method to determine if a resin is skinless is to look at theresin under magnification or take micro-photographs of resin particlesand observe if a continuous skin or pericellular membrane exists. In amicro-photograph, an observer can see into the internal area of theresin particles of this invention. The high porosity, friable particlesappear like a sponge with many openings in the surface of the resinparticle. These openings allow for fast plasticizer uptake and create afriable particle which is easily broken down into smaller units (primaryparticles).

The resin particles of this invention also have a fast powder mix timeas measured using a torque rheometer according to ASTM D-6373. The resinparticles of this invention have a powder mix time of less than about400 seconds, preferably less than 300 seconds, more preferably less than250 seconds.

The resins of this invention must also have good friability. Thefriability value of a resin is an indication of the relative ease withwhich grains break down into agglomerates and finally to primaryparticles. The lower a resin's friability value, the more desirable theresin. High friability values are known to relate to temporary fish-eyesand surface roughness in flexible extrudates. Fish-eyes are undesirableareas in a product, such as a film, which are areas of non-uniformity.This is especially important in powder extrusion and high plasticizerapplications. One method to test PVC resin for friability is to place agiven amount of resin in a mortar and grind the resin with a pestle. Thebetter the friability, the easier the resin particles will break apart.The friability is then subjectively graded on a scale of from 0 to 5,with 0 being very friable and equivalent to the best known PVC forfriability. A level of 5 is equivalent to a high quality film graderesin. Values between 0 and 5 are rated as to how they compare withreference standards which are blends of a 0 value resin and a 5 valueresin. The resins of this invention have a friability value of about 2or less, preferably they have a friability value of 1 or less, and morepreferably they have a friability value of 0.

For reference, make up standards using blends of Geon®92 (a skinlessspherical PVC resin produced by B. F. Goodrich according to the processof U.S. Pat. No. 3,706,722) and well known for its excellent friabilityand Geon®30 (a high quality film grade PVC resin with a skin producedand sold by B. F. Goodrich) as follows:

Reference Standard "0" is a mix of Geon 92: 100 parts and Geon 30: 0parts.

Reference Standard "1" is a mix of Geon 92: 80 parts and Geon 30: 20parts.

Reference Standard "2" is a mix of Geon 92: 60 parts and Geon 30: 40parts.

Reference Standard "3" is a mix of Geon 92: 40 parts and Geon 30: 60parts.

Reference Standard "4" is a mix of Geon 92: 20 parts and Geon 30: 80parts.

Reference Standard "5" is a mix of Geon 92: 0 parts and Geon 30: 100parts.

Compare the friability of the resin tested to the friability of thereference standards. Choose the standard which most closely correspondsto the test resin and report that standard as the friability of the testresin.

To further illustrate the present invention, the following specificexamples are given, it being understood that this is merely intended inan illustrative and not a limitative sense. In the examples, all partsand percents are by weight unless otherwise indicated.

EXAMPLE I

This Example is presented to demonstrate a process to produce theskinless resin of this invention. A 3 liter reactor equipped withagitation and cooling means was used in this Example. The followingpolymerization recipe was used:

    ______________________________________                                        Ingredient             Parts by Wt.                                           ______________________________________                                        Vinyl Chloride         100                                                    Water (demineralized)  182.1                                                  Polyacrylic Acid Dispersant                                                                          0.02                                                   NaOH                   0.005                                                  Isopropyl Alcohol      0.570                                                  Low Hydrolysis (55%) PVA                                                                             0.300                                                  Di-secondary Butyl Peroxydicarbonate                                                                 0.030                                                  Phenolic Shortstop     0.015                                                  ______________________________________                                    

The ingredients were charged according to the reactor charging proceduredisclosed in this specification. The reaction was conducted at 53° C.The NaOH was charged as a 2% solution in water after 15 minutes into thereaction (about 1% conversion). At 290 minutes the reaction wasterminated with the phenolic shortstop. The resin was removed from thereactor, stripped of residual monomer and dried to a free flowingpowder.

The resin particles were agglomerated, irregular shaped porous resinparticles with the following properties:

    ______________________________________                                        Weight average particle size                                                                        189 microns                                             Mercury porosity      0.437 cc/gm                                             Powder mix time       259 seconds                                             Shape factor          0.73                                                    Surface composition as measured by ESCA:                                      PVC                   67.9%                                                   Polyacrylic acid dispersant                                                                         22.5%                                                   Polyvinyl alcohol dispersant                                                                         9.6%                                                   ______________________________________                                    

The high amount of PVC on the surface is an indication of a skinlessresin. The low shape factor (0.73) is an indication of an irregularshape. The shape and skinless nature of the particles can also beobserved by referring to FIGS. 1, 2 and 3. FIG. 1 is a photomicrographof the resin particles produced in this Example I magnified 100 times,where the porous structure and irregular shape can be observed. FIG. 2is the same resin magnified 500 times. FIG. 3 is the same resinmagnified 5000 times. FIG. 3 shows the surface of one particle. Theinternal structure of the particle is visible along with theapproximately 1 micron or less size primary particles that go intomaking up the particle. As can be seen from FIG. 3, there is very littleskin on the resin. The high porosity (voids) is also visible from FIG.3. These voids are available to absorb high amounts of plasticizerquickly.

EXAMPLE II

This Example is presented as a further demonstration of a process toproduce the skinless resin of this invention. The recipe and conditionsare similar to those of Example I. A 3-liter reactor equipped withagitation and cooling means was used in this Example similar to ExampleI. The following polymerization recipe was used:

    ______________________________________                                        Ingredient             Parts by Weight                                        ______________________________________                                        Vinyl chloride         100                                                    Water (demineralized)  182.1                                                  Polyacrylic acid dispersant                                                                          0.02                                                   NaOH                   0.005                                                  Isopropyl alcohol      0.570                                                  Low hydrolysis (55%) PVA                                                                             0.300                                                  Di-secondary butyl Peroxydicarbonate                                                                 0.030                                                  Phenolic shortstop     0.010                                                  ______________________________________                                    

The ingredients were charged according to the reactor charging proceduredisclosed in this specification. The reaction was conducted at 53° C.The NaOH was charged as a 2% solution in water after 15 minutes into thereaction (about 1% conversion). At 350 minutes the reaction wasterminated with the phenolic shortstop. The resin was removed from thereactor, stripped of residual monomer and dried to a free flowingpowder.

The resin particles were agglomerated, irregular shaped resin particleswith the following properties:

    ______________________________________                                        Weight average particle size                                                                        175 microns                                             Mercury porosity      0.421 cc/gm                                             Powder mix time       245 seconds                                             Shape factor          0.77                                                    Surface composition as measured by ESCA:                                      PVC                   55.3%                                                   Polyacrylic acid dispersant                                                                          0%                                                     Polyvinyl alcohol dispersant                                                                        44.7%                                                   ______________________________________                                    

The high amount of PVC on the surface and the absence of the primarydispersant is an indication of a skinless resin. The low shape factor0.77 is an indication of an irregular shape. The shape and skinlessnature of the particles can also be observed by referring to FIGS. 4, 5and 6. FIG. 4 is a photomicrograph of the resin particle produced inthis Example II magnified 100 times, where the porous structure andirregular shape can be observed. FIG. 5 is the same resin magnified 500times. FIG. 6 is the same resin magnified 5000 times. FIG. 6 shows thesurface of one particle. The internal structure of the particle isvisible along with the primary particles which are about 1 micron orless in size, and go into making up the resin particles. As can be seenfrom FIG. 6, there is very little skin on the resin. The resin alsonoticeably has high porosity (voids) which are available to absorb highamounts of plasticizer quickly.

EXAMPLE III

This Example is presented to show the comparative properties ofskinlessness and shape of resins of this invention to a resin producedby the process of reference U.S. Pat. No. 3,706,722, Nelson, et al andto a resin produced by the mass process. The resin of Nelson, et al wasa standard production resin which is marketed as a skinless, highporosity resin. The photomicrographs in the reference Nelson, et al showthe resin to be relatively spherical in shape and to be porous.

    ______________________________________                                                    Mass      Nelson  Example Example                                 Property    Process   et al   I       II                                      ______________________________________                                        Shape factor                                                                              0.88      0.91    0.73    0.77                                    % PVC on surface                                                                          100%      27.9%   67.9%   55.3%                                   Agglomerated                                                                              No        No      Yes     Yes                                     ______________________________________                                    

As can be seen from the above comparison, the resins of this inventionhave higher % PVC on the surface of the resin thus indicating a muchhigher degree of skinlessness (about twice that of Nelson, et al resin).The resins of this invention are also agglomerated irregular shaped thushaving a lower shape factor than mass process resin or Nelson, et al'sresin. This shape factor and higher amount of skinlessness allows resinsof this invention to absorb plasticizer more quickly than Nelson et alresin, even at the same porosity levels. Mass resins, since there are nosurfactants present, will have 100% of the surface as PVC. Mass resinsare much more spherical than the agglomerated resins of this invention.The mass resins are also known for having low porosity as compared tosuspension resins.

EXAMPLE IV

This Example is presented to demonstrate an agglomerated, non-sphericalresin having a skin. FIGS. 7 and 8 represent a standard production PVCpipe resin having a skin and being agglomerated. FIG. 7 is amicrophotograph showing a standard suspension process produced PVC resinmagnified 100 times actual size. FIG. 8 is the same resin as is in FIG.7 except one of the particles is magnified 500 times actual size. As canbe seen, the resin has an essentially continuous skin covering the resinparticle. The skin is a graft polymer of the dispersant used with vinylchloride. The shape factor of the resin shown in FIGS. 7 and 8 is 0.76.

EXAMPLE V

This Example is presented to demonstrate an agglomerated, highly porous,non-spherical resin having a skin. FIGS. 9 and 10 represent a standardproduction PVC film grade resin having a skin and being agglomerated andhaving higher porosity than the resin of Example IV (FIGS. 7 and 8).FIG. 9 is a magnification of 100, whereas FIG. 10 is a 500 magnificationof actual size. Although the resin is porous, it can be seen that thereexists an essentially continuous skin covering the resin particle.

EXAMPLE VI

This Example is presented to show the novel resin of this inventionproduced by a preferred process and also the excellent properties of theresin. An 1100 gallon reactor equipped with agitation and cooling meanswas used in this Example. The following polymerization recipe was used:

    ______________________________________                                        Ingredient           Parts by Weight                                          ______________________________________                                        Vinyl chloride       100                                                      Water (dimineralized)                                                                              150                                                      Polyacrylic acid dispersant                                                                        0.02                                                     PVA (55% hydrolysized)                                                                             0.30                                                     NaOH                 0.0025                                                   Di(2-ethylhexyl)peroxydicarbonate                                                                  0.045                                                    ______________________________________                                    

The ingredients were charged according to the Reactor Charging Proceduredisclosed in this specification except that the free radical catalyst(di(2-ethylhexyl)peroxydicarbonate) was charged into the mixture ofwater and polyacrylic acid dispersant before monomer was charged. ThePVA was charged into the vinyl monomer. The reaction was conducted at53° C. The NaOH was charged as a 2% solution in water after 15 minutesinto the reaction (about 1% conversion). At 350 minutes the reaction wasshortstopped with the phenolic shortstop. The resin was removed from thereactor, stripped of residual monomer and dried to a free flowingpowder.

The resin particles were skinless, agglomerated, irregular shaped porousresin particles. The resin had the following properties:

    ______________________________________                                        Weight average particle size                                                                        187 microns                                             Mercury porosity      0.524 cc/gm                                             Powder mix time       155 seconds                                             Friability            0+                                                      ______________________________________                                    

From the above results it can be seen that the resin has a high porosityand an exceptionally short powder mix time indicating that the skinlessresin can very quickly absorb large amounts of plasticizer. Thefriability is also excellent, indicating that the resin particles willeasily break apart when stress is applied thus resulting in lowfish-eyes in the finished product. These excellent properties areobtained even though the reaction was run to 72% conversion.

EXAMPLE VII

This Example used the same 1100 gallon reactor and the chargingprocedure and polymerization recipe as Example VI, except that 0.005part by weight of NaOH per 100 parts by weight monomer was used todesorb the primary dispersant.

The resin particles were skinless, agglomerated, irregular shaped porousresin particles with the following properties:

    ______________________________________                                        Weight average particle size                                                                        238 microns                                             Mercury Porosity      0.466 cc/gm                                             Powder mix time       173                                                     Friability            0                                                       ______________________________________                                    

The properties show a resin having excellent friability and fast powdermix times.

EXAMPLE VIII

This Example is presented to show the fast dry-up times and cycle timeswhen this resin is mixed with high levels of polymeric plasticizer. Theresin of Example VII is compared to a commercial resin produced by theprocess described in U.S. Pat. No. 3,706,722 to Nelson, et al and to acommercial high porosity (0.38) film grade resin having a skin. Theresins were mixed in a Henschel mixer with 120 parts by weight ofpolymeric plasticizer per 100 parts by weight of resin. The followingresults were obtained:

    ______________________________________                                                                            Powder                                                                        Flow                                      Resin      Dry-up Time Cycle Time   Rating.sup.2                              ______________________________________                                        Nelson et al                                                                             3 min. 38 sec..sup.1                                                                      15 min. 46 sec..sup.1                                                                      3.sup.1                                   Conventional                                                                             4 min. 4 sec.                                                                             14 min 5 sec.                                                                              4.sup.                                    high porosity                                                                 film grade                                                                    Example VII                                                                              2 min. 57 sec..sup.1                                                                      11 min. 51 sec..sup.1                                                                      3.sup.1                                   (this invention)                                                              ______________________________________                                         .sup.1 Average of 2 runs                                                      .sup.2 A powder flow rating of 3 indicates lumpy, free flowing. A powder      flow rating of 4 indicates lumpy, wet.                                   

EXAMPLE IX

This Example is presented to compare the level of fish-eyes in the resinof Example VI of this invention with the level of fish-eyes in the resinof Nelson, et al (U.S. Pat. No. 3,706,722).

    ______________________________________                                                                 Example VI Resin                                     Test      Nelson et al Resin                                                                           (this invention)                                     ______________________________________                                        6 inch    4       Fish-eye   0     Fish-eye                                   Mill Fish-eye                                                                           1       Fines      3     Fines                                                5       Total      3     Total                                      8 inch    2       Fish-eye   0     Fish-eye                                   Mill Fish-eye                                                                           1       Fines      0     Fines                                                3       Total      0     Total                                      ______________________________________                                    

This Example demonstrates that the resin of this invention is excellentfor low fish-eye. The resin of Nelson, et al has been recognized in theindustry as being an excellent choice for low fish-eye. The resin ofthis invention is superior to the Nelson, et al resin for low fish-eye,thus indicating an excellent resin.

EXAMPLE X

This Example is presented to show an alternate method of producing lowskin resins of this invention whereby low levels of the ion sensitiveprimary dispersants are used and NaOH is not used to desorb the primarydispersant. In this Example the following polymerization recipe andconditions were used:

    ______________________________________                                        Ingredient             Parts by Weight                                        ______________________________________                                        Vinyl chloride         100                                                    Water (demineralized)  150                                                    Polyacrylic acid dispersant                                                                          0.025                                                  Low hydrolysis (55%) PVA                                                                             0.600                                                  Di-secondary butyl peroxydicarbonate                                                                 0.022                                                  Phenolic shortstop     0.010                                                  ______________________________________                                    

The reactor used and the charging procedure used were the same as inExample VI except that NaOH was not used to desorb the polyacrylic aciddispersant off the monomer droplets.

The resin produced was porous, low-skin, agglomerated and non-sphericaland had the following properties:

    ______________________________________                                        Weight average particle size                                                                        313 microns                                             Mercury porosity      0.428 cc/g                                              Powder mix time       246 seconds                                             ______________________________________                                    

From the microphotographs in FIGS. 11 and 12, it can be seen that theparticles of this Example are non-spherical, agglomerated particles.FIG. 11 is a photomicrograph of the resin magnified 100 times actualsize. FIG. 12 is a particle of FIG. 11 magnified to 500 times actualsize. From FIG. 12 it can be seen that the particle has low-skin, thatis, there are significantly large areas on the surface which have noskin and are sponge-like in appearance. There are also areas which havea skin on the surface of the particle. From FIG. 12 one can easilydetermine the difference in the degree of skin between this low-skinparticle and the skinless particles of Examples I and II (FIGS. 2 and5). The resin of this Example also exhibits equivalent friability andfish-eye levels to the Example VI resin.

EXAMPLE XI

This Example is presented to show an additional alternate method ofproducing the resins of this invention. In this Example a 55 literreactor was used which was equipped with agitation and cooling means.The polymerization recipe used was as follows:

    ______________________________________                                                      Parts by Weight                                                 Ingredient      Run 1      Run 2   Run 3                                      ______________________________________                                        Vinyl chloride  100        100     100                                        Water (demineralized)                                                                         150        150     150                                        Sorbitan monooleate                                                                           0.3        0.3     0.3                                        PVA (55% hydrolyzed)                                                                          0.3        0.2     0.1                                        Polyacrylic acid                                                                              0.0325     0.040   0.040                                      dispersant                                                                    Di-secondary butyl                                                                            0.030      0.030   0.030                                      peroxydicarbonate                                                             Phenolic shortstop                                                                            0.010      0.010   0.010                                      The resins were all skinless, agglomerated resins                             having the following properties:                                              Weight average particle                                                                       145        186     232                                        size (micron)                                                                 Mercury porosity (cc/g)                                                                       0.503      0.420   0.397                                      Powder mix time (seconds)                                                                     163        204     177                                        Friability value                                                                              0          0+      1+                                         ______________________________________                                    

In all of the Examples which show the polymerization processes of thisinvention, the reactor buildup was from very low to none. This is incontrast to the process of Nelson, et al, which gives very high amountsof polymer buildup on the internal surfaces of the polymerizationequipment. The very nature of the phase inversion process of Nelson, etal is believed to be detrimental to keeping the polymerization equipmentclean. The process of this invention gives clean reactors which are ableto be used for several polymerization runs before being shut down forcleaning.

The resins of this invention have many uses in end product applicationswhere PVC is used. Their principal application is in film gradeapplications because of their high porosity and friability. Anywhere PVCresins are needed that require them to absorb a large amount ofplasticizer quickly, the resins of this invention would be an excellentchoice.

I claim:
 1. An agitated aqueous suspension process for producing porous,substantially skinless, agglomerated polyvinyl chloride resin particlescomprising polymerizing vinyl monomer in the presence of a dispersantsystem comprising (a) from about 0.02 to about 0.06 part by weight per100 parts by weight monomer of an ion sensitive primary dispersantcapable of thickening water; (b) from about 0.2 to about 0.4 part byweight of non-polyethylene oxide containing secondary dispersant; and(c) from about 0.1 to about 0.3 part by weight per 100 parts by weightvinyl monomer of a polyvinyl acetate secondary dispersant having ahydrolysis level less than 70%, said resin particles having a mercuryporosity of from about 0.1 cc/g to about 0.7 cc/g, and a particle sizeof from about 70 microns to about 1000 microns, and a friability of lessthan about 2, and a powder mix time of less than about 400 seconds, anda shape factor less than about 0.85 and wherein greater than about 20%of the area of the surface of said particle is PVC as measured by ESCA.2. A process of claim 1 wherein said non-polyethylene oxide containingdispersant is selected from the group consisting of sorbitan trioleate,sorbitan tristearate, sorbitan monooleate, sorbitan monopalmitate,glycerol monooleate, glycerol monostearate, and triglycerol monooleate.3. A process of claim 2 wherein said primary dispersant is a lightlycrosslinked interpolymer of acrylic acid.
 4. A process of claim 3wherein said polyvinyl acetate secondary dispersant has a hydrolysislevel less than 55%.
 5. A process of claim 4 wherein said vinyl monomeris vinyl chloride.